The present invention relates to a valve-open-close mechanism operated by an electromagnetic actuator and used mainly in an automotive internal combustion engine.
A conventional valve-open-close mechanism for automotive internal combustion engines is disclosed e.g. in Japanese patent publication 11-93629. Referring to FIG. 1, which shows one embodiment of the present invention, an electromagnetic actuator 4 includes a pair of electromagnets 6, 7 each made up of a stator 5 and a coil 18 that are opposed to each other by with a gap S therebetween. An armature 3 is disposed in the gap 10 so as to be reciprocable between two electromagnets 6, 7. A first stem 15 for transmitting the movement of the armature 3 from the electromagnet 6 toward the one electromagnet 7 to external is provided on one surface of the armature 3.
The electromagnetic actuator 4 is housed in a housing 8 fixed in an internal combustion engine 19. The tip of the first stem 15 of the electromagnetic actuator 4 is brought into abutment with the tip of the valve 9 so that by moving the armature 3 toward the electromagnet 7, the first stem 15 pushes the valve 9 to open it. Further, in order to impart a biasing force for opening the valve 9, a retainer 13 is provided on the valve 9, and a first return spring 2 is mounted between the retainer 13 and the internal combustion engine body 19; a second stem 14 is provided on a surface opposite to the surface of the armature 3 on which is provided the first stem 15; and the retainer 13 is provided on the second stem 14, and a second return spring 1 for imparting a biasing force in the direction in which the second stem 14 pushes the armature 3 is mounted between the retainer 13 and the housing 8.
In this valve-open-close mechanism, the weights of directly driven parts during actuation have a direct influence on the driving power consumption of the electromagnetic actuator 4 as an inertia weight. Since the driving power is normally supplied from an on-board battery, an increase in the power consumption is not preferable. Also, the weights of other parts that are not directly driven will also has a direct influence on the total weight of the internal combustion engine. Thus, if it is used in an automobile, it will have a direct influence on the fuel consumption.
But heretofore, for these parts, as disclosed in the above publication, no consideration has been given regarding the material and lightening of the weight and iron-family or steel-family materials having a specific weight of 7 to 8 are used.
In attempting to lighten the weight of each of these parts, a reduction in the mechanical strength of each part will result from lightening of the weight. For the retainer 3, mechanical strength to withstand a load from the coil spring 1 or 2 is required.
An object of this invention is to provide a retainer which can sufficiently withstand a spring load even if its weight is reduced.
In order to solve this object, according to the present invention, the retainer comprises a boss and a surrounding spring support, and in view of the fact that the corner portion extending from the spring support to the boss is the weakest portion subjected to the spring load, the corner portion of the retainer is formed to be arcuate. Since it is arcuate, stress concentration is relieved, so that chipping at the corner portion is eliminated.
According to this invention, there is provided the valve-open-close mechanism for an internal combustion wherein the electromagnetic actuator comprises a pair of electromagnets each made up of a stator and a coil opposed to each other with a gap therebetween; an armature disposed in the gap so as to be reciprocable between the pair of electromagnets by driving the electromagnets; and a first stem for transmitting to external the movement of the armature from one electromagnet toward the other electromagnet; the electromagnetic actuator being housed in a housing mounted to an internal combustion engine body; the armature being moved from the one electromagnet toward the other electromagnet, so that the first stem opens the valve by pushing the valve; the electromagnetic actuator further comprising a first retainer provided on the valve for imparting a biasing force to the valve for a valve-closing operation, and a first return spring mounted between the first retainer and the internal combustion engine body; a second stem provided at a surface of the armature on the side not coupled to the first stem; and a second retainer provided on the second stem, and a second return spring mounted between the second retainer and the housing for imparting a biasing force.
According to this invention, the radius of curvature R of the arc of the corner portion is derived from the following formula:
K=Pxc3x97dxc3x97(1xe2x88x920.4R)xe2x89xa6Cxc3x97t=Q[Nxc2x7mm]
wherein
Q: Allowable stress for the retainer 13
P: Spring load produced when spring 1, 2 is compressed to the limit
d: Wire diameter (mm) of spring 1, 2
t: Fatigue strength of material used for retainer
C: Constant
Here, the permissible stress level Q of the retainer is, as will be apparent from the above formula, a value determined by the material, and is obtained from the experiment results as a numerical value which is correlated with the stress state (See the below-described mechanical strength test for the retainer.). Pxc3x97d is a stress level applied to the retainer and (1xe2x88x920.4R) is an approximate formula for stress concentration defined in a non-dimension. They were obtained by this kind of experiments. R is a numerical value in millimeter as a unit.
Since arcuation of the corner portion achieves lowering of stress concentration, it is necessary not to form steps at the continuous portion between the end of the arcuate corner portion and the spring abutting surface of the retainer and the end of the boss peripheral surface in view of cut-out effect. In particular, it is preferable that the corner portion has such an arcuate shape that the curvature gradually increases toward the abutting surface and the peripheral surface of the boss.
The retainer is preferably formed of a powder molded article such as an aluminum alloy hardened material by forging. The arcuate shape of the corner portion may be formed simultaneously with the formation of the retainer or formed by machining after molding.
At least one of the first stem, second stem, housing, valve, first return coil spring and second return coil spring may be formed of a metal smaller in specific weight than iron, its alloy, an alloy reinforced with aggregate and having a smaller specific weight than iron, a ceramics, a fiber- or whisker-strengthened ceramics.
If a metal smaller in specific weight than an iron-family member which has a specific weight of 7-8, its alloy, an alloy reinforced with aggregate, a ceramics, or a fiber- or whisker-strengthened ceramic material, which has heretofore been used, is used for the parts, this leads to reduction in the inertia weight and total weight.
According to the present invention, the first return coil spring or second return coil spring is made of an alloy steel containing 0.55-0.70 wt % of C, 1.0-2.2 wt % of Si, 1 wt % or under of Cr, 1 wt % or under of Mn, 0.2 wt % or under of V, having a tensile strength of 1960 N/mm2 or over, containing inclusions of a size of 25 xcexcm or under, and having a tempered martensitic structure.
Further, besides the desired spring properties, for achieving a reduction in weight, the first return spring or second return spring is made of a titanium alloy comprising a total of 13 wt % or over of Al and V, having a tensile strength of 1500 N/mm2 or over and having a surface coating having a good wear resistance.
Furthermore, in order to achieve a similar object, the first return spring or second return spring is made of an aluminum alloy containing a total of 5 wt % or more of Cu, Mg and Zn, having long crystal particles having an aspect ratio of the crystal particle diameter of 3 or over, and a tensile strength of 600 N/mm2 or over.
Also, while the valve comprises a marginal portion and a stem portion, in order to maintain heat resistance of the marginal portion and reduce the weight, the marginal portion may be made from a heat-resistant steel alloy and the stem portion may be made from an aluminum alloy sintered member formed by powder molding.
Also, in order to achieve a similar object, the valve may be made from a ceramic material whose major component is silicon nitride or SIALON.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: